The cat has long been a standard animal for anatomical and acute physiological studies of muscle function and motor control at the spinal cord level. In this project, a wide variety of traditional and novel kinesiological techniques are being used to study motor tasks in unanesthetized, normally behaving cats, including computer-aided reconstruction of skeletal movement from videotape, multiaxis force plates, chronically implanted nerve cuff and EMG electrodes, and strain and length transducers. The major focus has been the study of hindlimb muscles and their afferent and efferent control during walking. Other hindlimb movements studied include jumping, paw shaking, scratching, and reflexes to cutaneous nerve stimulation during normal and decerebrate walking. In a collaborative study, stimilar data are being collected from a large number of neck muscles. The major objective is to correlate patterns of usage with the complex mechanics and compartmentalization and proprioceptive specializations of thse muscles. A major theme emerging from these experiments is a concept of "Task Groups," which denotes the segragation and specialization of sensorimotor systems to groups kinematically homogenous tasks in an optimal manner. This is particulary apparent in multiarticular muscles, which in some cases use indepedent subdivisions of their alpha motoneuron pool to accomplish kinematically diverse tasks. Some of these bifunctional muscles have been to have a heretofore overlooked internal architecture consisting of short, parallel muscle fibers in series, which poses additional questions regarding their coordination. Current work asks how well these notions extend to other bifunctional muscles and other programs (such as reflexes) and is examining how much anatomical and physiological independence exists between task groups, in both the spinal cord and in the muscle.